The field of the invention relates to controlling the wheel slip of a driven wheel coupled to an internal combustion engine.
When a vehicle (such as an automobile, truck or motorcycle) accelerates over a slippery surface, the engine torque applied to the driven wheel may cause abrupt acceleration or wheel spin. A temporary loss in vehicle control may result.
An approach towards solving the problem of wheel slip is disclosed in German patents 2058819 and 2832739 wherein the engine throttle is controlled in inverse relation to a measured difference in rotation between a driven wheel and a non-driven wheel. U.S. Pat. No. 4,554,990 issued to Kamiya et al discloses a control system wherein the difference in rotation between a driven wheel and a non-driven wheel is used as a feedback variable. The other feedback variables are a signal related to actual throttle position, and a signal related to throttle position commanded by a vehicle operator.
The inventors herein have recognized numerous disadvantages of these prior approaches. One disadvantage is that torque is removed from the drive wheel by controlling an engine input (throttle). Thus, torque is not removed from the drive wheel until after time delay through the engine is incurred. Another disadvantage is that the feedback variable for engine torque output is derived from wheel speed. This feedback variable is therefore delayed by a time delay through the engine and drivetrain resulting in a feedback loop with poor transient response time.